Municipal wastes will typically include materials of widely varying physical characteristics. These may include fibrous materials, such as paper, cardboard and rags, plastic materials, glass, wire, light gauge metallic containers, and relatively heavy, infrangible materials such as heavy metal pipes and iron castings. It is generally desirable to separate the relatively infrangible materials from those which may be readily broken down to a small particle size, reduce the latter in an aqueous medium and pump the resulting slurry to further treatment stages.
This has conventionally required sorting the waste material prior to reducing the frangible fraction to a size capable of being suspended in an aqueous medium. Additionally, even though the relatively infrangible portion of the waste is removed, the disparate characteristics of the remaining fraction render in them not readily amenable to reduction in a single treatment. This is particularly true where the waste materials contain a relatively high proportion of stringy materials, such as rags, tubing, and the like, as is usually found in waste materials received from hospitals.
It has, therefore, been long recognized that it would be highly desirable to combine in one treatment the functions of separating the relatively frangible and infrangible portions of the waste material and at the same time efficiently reducing the frangible portion to a particulate state, even though the physical characteristics of the frangible portion are quite dissimilar.